Conventionally, a coated cutting tool formed by depositing, through chemical vapor deposition, a coating layer onto a surface of a substrate comprised of, for example, a cemented carbide, is well known for being used for the cutting of steel, cast iron, etc. A coating layer generally consists of a single layer of one kind selected from among, for example, Ti-based compounds (carbides, nitrides, carbonitrides, carbonates and carboxynitrides) and aluminum oxide, or consists of multiple layers of two or more kinds selected therefrom, and such coating layer has a total thickness of 3 to 20 μm.
Patent Document 1 discloses a cutting tool in which, on a surface of a tool substrate made of a WC group cemented carbide or TiCN group cermet, a Ti compound layer is formed as a lower layer and an Al2O3 layer is provided as an upper layer. Patent Document 1 indicates that such Al2O3 layer has a κ type or θ type crystal structure in the state of having been formed through chemical vapor deposition and has been subjected to modification treatment so as to have, through heat treatment after chemical vapor deposition, an α-type crystal structure, and also indicates that such Al2O3 layer shows an X-ray diffraction chart which shows clear diffraction peaks on a (006) plane and a (018) plane in an X-ray diffraction measurement.